Pests

a chips Greenfly and black th are among the most common ofthe greenhouse insect pests. They normally cluster together and arc easily seen with the naked eye. Aphids are sap suckers and if present in large numbers their feeding soon checks the plant's growth; they are also major carriers o! virus diseases. They can be controlled with a variety of chemicals.

earwigs These are likely to damage open flowers by eating the petals; they are particularly active at night. The hollow ends of garden canes are common hiding places, and earwigs can be successfully controlled by trapping. Several small pots, hall filled with wood wool, should be inverted over garden canes within the greenhouse or frame. The earwigs hide in the wood wool and are then easily shaken from it and killed.

leaf miner The maggot of the leaf miner tunnels between the upper and lower layers ot the leaf before it pupates; this results in unsightly foliage, if no action is taken the fly that emerges from the pupa stage w ill lay more eggs. If only a few leaves are affected remove them by hand and burn them, Otherwise control them with a suitable insecticidal spray, repeating this treatment twice at fortnightly intervals.

red SPIDER mites These are sap suckers and attack plants from the underside of the leaves. The very small red mites are usually visible because ot' their delicate webs and their large numbers. The sucking causes the leaf to become mottled and then yellow. Spraying needs to he very thorough and directed particularly at the underside of the leaf: for this reason fumigants are preferred by many gardeners The

scale insects Troublesome pests, scale insects arc a particular nuisance on leaves and stems ot" house plants. The brown soft scale is the most common and is about 3 mm (i in) long. The adults do not move and infestation often begins on the underside ot the leaves. If only small numbers arc present they may be removed with cotton wool dipped in methylated spirits. Alternatively use a systemic insecticide, a type that is absorbed by a plant through its leaves or from the soil and spreads throughout the plant's tissues.

slugs and snails These cotii mon garden pests relish some species of seedlings and young plants, and breed wherever rubbish is left lying around. Clean greenhouses and cold frames get few intruders. Slug baits are effective it kept dry, and if you have overwintering lettuce they should be used as a routine measure.

whitefly A pest of many plants under glass. The adult flies, about i mm ( ^ 111) long, normally inhabit the topmost leaves and rise into the air when the plants are disturbed. The larvae suck sap and excrete a honeydew 011 tn fruit and foliage, and this encourages the growth of a dark sooty

Whiteflv ihe flies are seen here with examples of the pupal stage

mould. Fumigants are usually the best means of control, but it they fail to achieve good results the introduction of the parasite Encarsia J'ormosa should be considered (see below),

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